We developed techniques for efficient DNA-mediated transfer of genes into primate cells and used these techniques to search for DNA sequences that regulate mammalian cell growth. Studies on growth-stimulatory genes focused on complementation of mutant human c-ras by the adenovirus E1A gene, and involved efforts to detect complementation of c-ras by gene(s) present in preneoplastic or tumor cells. Studies on growth-inhibitory genes focused on sequences present in WI38 human embryo fibroblast DNA that are capable of slowing HeLa S3 cell growth. It was shown that WI38 growth-inhibitory sequences are active in primary and secondary gene transfer experiments; in addition, growth-inhibitory sequences were detected in a cosmid library derived from WI38 DNA. Continuing efforts to improve gene transfer technology included development of improved selection conditions for methotrexate-resistance vectors, further application of a novel vector system based on the bacteriophage lambda lysogenic cycle, and construction of retrovirus vectors carrying dihydrofolate reductase or chloramphenicol acetyltransferase genes.